Recently, since development of integrated circuits (IC) has been down sized to nano-scale, application to nano-scale elements becomes more and more popular. Among all inventions, short-wavelength light emitting devices, such as laser diodes (LD) and light emitting diodes (LED), have been the mainstream. For development of short-wavelength light emitting devices, III-V compounds semiconductors are the common materials for manufacturing LED. However, with development of new systematic materials, II-VI compounds semiconductors are valued again. In practice, Zinc oxide (ZnO) has advantages of low cost and easy synthesis. Hence, study on ZnO is a hot topic today, especially on the ZnO nanorods.
ZnO has a direct band-gap of 3.37 eV which is higher than other high direct band-gap semiconductor materials. In addition, ZnO has higher excitation binding energy (excitation binding energy of Gallium Nitride (GaN) is around 20 meV while that of ZnO is much higher and about 60 meV.). Therefore, its lighting efficiency is higher than other materials under room temperature. During recent years, a lot of reports on study of ZnO show that it can be applied to short-wavelength elements and laser diodes due to the good lighting efficiency. Since data accessing can be improved by using ultraviolet (UV) laser, application of ZnO to UV laser source has a great potential. For ZnO, membrane elements are very popular.
Besides, another main direction of development of ZnO is one-dimensional nanorods (nanowires). Scientists can grow highly aligned nanorod array successfully. With photoluminescence, UV laser is excited out of the nanorods. Although UV laser can be commercialized in many ways, how to enhance light extraction and control light escape angle of nanorods still has two problems to be solved. Otherwise, lighting efficiency will be significantly affected.
Therefore, the present invention provides a solution to the problems mentioned above. Via the invention, light extraction of a light emitting device can be enhanced.